Passenger vehicle wheels have long been manufactured from sheet and plate steel materials wherein the rim is rolled formed to provide a drop center well type rim for receiving a tubeless pneumatic tire, and a stamped sheet metal disc (also known as a wheel body or wheel spider) is press fit into and welded to the inner periphery of the rim to complete a wheel assembly adapted for mounting to a vehicle axial spindle, hub or drum-hub. Such vehicle wheels conventionally include a circular array of disc bolt openings adpated to receive mounting studs for mounting the wheel to a vehicle, and a center-pilot opening adapted to be received over the wheel spindle.
It has been and remains conventional practice in industry to attempt to form a bolt mounting circle and center-pilot openings coaxially with each other and with the tire rim bead seats with the goal thus being a perfect true-running wheel. A number of techniques have been proposed and employed for accomplishing this result, including formation of the bolt and center openings with a single punching tool set operating on a rim and disc assembly while locating off of the bead seat, machining the center opening while locating off of the preformed bolt-mounting openings, and/or circumferentially permanently deforming the rim bead seats while locating off of the bolt-mounting and/or center pilot openings. For example, Gregg U.S. Pat. No. 3,688,373 discloses apparatus for rounding and forming vehicle wheels. It is also conventional practice in the manufacture of such wheels to machine the inside surface or ID of the rough formed center pilot opening while locating off of the bead seats to obtain concentricity between the center openings and the bead seats.
However, in manufacturing operations set up for mass production of sheet metal and plate fabricated components such as the aforementioned steel passenger vehicle wheels, it is often more economical, and in some cases more accurate, to employ metal piercing, punching and/or shaving operations to form through openings in the disc metal, such as the aforementioned bolt mounting circle and center-pilot openings in the wheel disc, rather than to form these openings by machining operations such as drilling, reaming, boring, etc. due, for example, to existing investment in stamping and punch press equipment as well as the associated facility for designing, making and maintaining the tooling for such equipment.
One example of utilizing piercing punch equipment in wheel manufacture is set forth in the Daudi et al U.S. Pat. Nos. 4,279,287 and 4,354,407, both assigned to the assignee hereof, which disclose a departure from the conventional practice of attempting to form a true-running wheel. These patents addressed the problem of radial and run-out and/or radial force variations in a pneumatic tire and wheel assembly by intentionally forming the bolt-mounting and/or center-pilot openings in the wheel disc at the time of wheel manufacture on an axis which is eccentrically offset from the average axis of the bead seats on the wheel rim. This offset is in the direction and amount which is predetermined to locate the low point or high point of the first harmonic of bead seat radial run-out circumferentially adjacent to a selected location on the wheel rim. In the preferred wheel forming apparatus disclosed in the above-noted Daudi et al U.S. Patents, the bolt and center-pilot openings are formed by separate punches fixedly mounted on a single punch assembly which simultaneously punch-forms all of the openings in a wheel disc while the wheel is located by fixturing the same about the rim bead seats.
However, it has been found that a particular problem is encountered in connection with utilizing the punch-formed center pilot opening in wheel disc for fixturing the wheel assembly in manufacturing, testing and/or vehicle assembly operations performed after punching. With the punching tool hitherto conventionally in use, typically the ID of the punching hole is characterized by two contrasting peripheral surface portions: (1) a relatively smooth, cylindrical surface condition measured from the point of punch initial impact on the steel stock and extending axially in the direction of punch-through motion for a distance equal to 25 to 50% of the thickness of the material being punched; (2) the balance of the hole surface extending to the opposite face of the punched material is characterized by a "break away" configuration, i.e., a jagged or torn surface of generally frusto-conical contour diverging radially outwardly or converging radially inwardly of the hole axis in the direction of the material removal by the punch. A similar and complimentary pattern may be observed on the outer periphery or OD of the scrap piece or "slug" removed from the disc by the punch during its strike through. This punch-formed ID surface of the center pilot opening has been found to create a problem when, inter alia, the finished wheel assembly is subsequently mounted in a wheel balacing machine wherein the wheel is fixtured by a chuck collet or mandrel which engages the ID of the center pilot opening. Undesirable variations from true center mounting occurred when dealing with "true-center" wheels, probably due to insufficient true surface area on the ID of the center pilot opening as well as the irregularities in the break away portion of the ID surface.
Of course, this center pilot problem could have been overcome by employing additional machining operations after the punching operations, but at a significant cost penalty. Another approach to the solution of this problem was to employ a shearing or shaving tool operation subsequent to the punching operation, a multi-step procedure which still entailed a cost penalty.
In an attempt to reduce this cost penalty, a multi-step pierce and shave combination tool of the prior art was tested in order to punch the center hole and then follow through with an ID shaving operation with a single stepped tool using a single stroke of the punch press. This tool was formed with a typical punch nose configuration i.e., a flat end strike face perpendicular to the axis of the punch and terminating at its outer edge in a cylindrical side face which extended axially of the tool away from the end face by a distance greater than the material thickness of the disc center hole margin area. The punch shank surface terminated at a shaving shoulder, also formed perpendicular to the punch axis and extending radially outwardly from the punch shank surface to a cylindrical shaving surface having an outer diamter slightly greater than the punch shank diameter. The shaving step shoulder performed a shaving operation on the previously punch-formed surface in order to impart a truer, more cylindrical and smoother ID to the center pilot opening.
However, this attempted solution to improving the center hole surface in turn created its own problem. It was found that the metal removed by the shaving shoulder during its strike-through formed a ring of scrap metal separate and detached from the punch slug. Although the punch slug would readily clear itself from the punch press by dropping through the scrap chute in the button retainer of the press, the shave-formed ring was found to either cling to the punch shank of the tool after the tool was retracted from the disc center hole or, if the back out stroke of the punch was operable to snag the ring on the disc hole surface, the ring would be stripped from the punch shank. The scrap ring would haphazardly drop onto the button surface and remain hung up on the punch button rather than dropping through the scrap chute. This in turn necessitated a scrap clean up operation after each center hole forming operation, with a concommittment cost penalty, and/or the possbility of tool or part damage should a scrap ring inadvertently remain in the punch apparatus.
Other prior art patents which are of interest to wheel manufacture of the type under consideration are U.S. Pat. Nos. 4,573,338; 4,646,434; 4,733,448 and 4,736,611, also assigned to the assignee hereof (which are incorporated herein by reference) and the references cited therein.